Prev: Elementary Mathematics From An Advanced Standpoint
Next: Integrals and Polynomials
From: Torsten Hennig on 8 Jun 2010 02:39
> A reservoir is being emptied, and the quantity of
> water, V m ^ 3 ,
> remaining in the reservoir t days after it starts to
> empty is given by V
> (t) = 10 ^ 3 * (90 − t) ^ 3.
>
> After what time is the reservoir being emptied at 3 *
> 10 ^ 5 m ^ 3 / day?
>
> -3 * 10 ^ 5 = -3 000 * (90 - t) ^ 2
> 100 = (90 - t) ^ 2
> +/- 10 = 90 - t
> t = 80, 100
>
> Currently, for me, these two values represent the
> days when dV / dt = 3 *
> 10 ^ 5 m ^ 3 *and that's all*. I'm not sure how to
> answer the question;
> it implies that there is only one time. The book's
> answer is 80 days -
> why?
>
> TIA,
> Albert

Since the reservoir is empty after 90 days, there
are positive flow rates only for times < 90 days ...

Best wishes
Torsten.
From: Fred Nurk on 8 Jun 2010 07:20
bert wrote:
> <snip>
> Do you suppose that dV/dt at t = 100 could have any more realistic
> interpretation than V at t = 100?

I get it now; thank you to both of you.

Fred
 | 
Pages: 1
Prev: Elementary Mathematics From An Advanced Standpoint
Next: Integrals and Polynomials